1. Field of the Invention
The present invention relates to an optical semiconductor device in which a light of the same phase and the same wavelength as an incident ray is inductively emitted to amplify the incident ray for producing a laser beam.
2. Description of the Prior Art
In a usual semiconductor device 40 of a gain and waveguide type stripe structure, as shown in FIG. 6, when an electric current is applied in a width or a stripe width S of an anode electrode 41, thereof, the electric current flows through a semiconductor region 42, i.e. p-type semiconductor region in this case to diverge laterally and transversely. Therefore, carriers injected into an active region 44 are diffused laterally and transversly away from the stripe width. As a result, the mountain-shaped density distribution of the injected carriers is formed with the stripe region located at the center. In case of the stripe width smaller than approximately 10 .mu.m, the injected carriers can be consumed effectively. Thus, even in an attempt to produce the near field pattern using a light of the basic mode (O-order mode), an output power of that light can be enhanced efficiently.
However, when the stripe width is set broad (larger than 10 .mu.m), the current density flowing vertically downward through the stripe width is lowered, and hence the balance between that non-diverging current density and the diverging current density (i.e., distribution ratio defining the mountain-shape) is lost and a central portion of the distribution curve of current density becomes flat as shown in FIG. 7.
The current density distribution having such a characteristic brings about carriers or gain which is needless and detrimental to excitation to be solely based on the basic mode. More specifically, in the stripe width region, there occur both a portion where the carriers are excessive and a portion where they are deficient, which will cause saturation of output power. The portion where the carriers are excessive causes heat generation, and hence a service life of the semiconductor light amplifier itself is shortened. Further, since the output power cannot have the ideal distribution as shown in FIG. 4, both of the carrier density distribution and the gain distribution exhibit characteristics similar to that of the current density distribution, as shown in FIG. 7.